1. Field of the Invention
The invention relates to a self-lubricating fuel composition having a powdered coal and hydrocarbon fraction basis.
The world coal reserves greatly exceed the reserves of all the other fossile fuels put together, including even the oil shales and sands. So attention is turned towards an increased use of these reserves.
The use of coal as a fuel raises transport and even combustion problems. The ideal would be to have coal available in the form of a pumpable fluid, having storage and transport and combustion characteristics similar to those of heavy fuel oil.
2. Description of the Prior Art
A certain amount of work has been done for providing a simple solution, in so far as its principle is concerned: it is a question of dispersing powdered coal in a hydrocarbon fraction, such for example as heavy fuel oils.
However the use of simple mixtures of powdered coal and heavy oil raises numerous problems, such as the sedimentation of the coal during storage and difficult pumping due to the high viscosity of the concentrated suspension.
The use of numerous additives has been suggested for stabilizing the coal-oil suspensions. Thus, a series of Japanese patents, Nos. 7953106, 7953107, 7953108 of 1977 and the U.S. Pat. No. 4,130,401 of 1978 describes the use of polythylene glycol or polypropylene glycol or copolymers thereof. The U.S. Pat. No. 4,162,143 of 1978 relates to the use of alkylaryl sulfonates or quaternary ammoniums.
In numerous cases, the addition of a small amount of water is favorable to the stabilization of these suspensions. The stabilizing effect is however accompanied by an increase of the viscosity of the oil-coal mixtures and consequently an increase of the pressure losses during pumping.